A 502 error is typically a Bad Gateway error. You can find common troubleshooting items at the link below however it may require a session with a network person to narrow it down. The first step I would take is to try and log in to that vCenter from the machine that is running the ESXQuery.
I have the esxquery tool being run by a server admin remotely and was assured that there is no issues logging into the virtual center from the source server.
I'll ask again about any possible proxy issues or network issues.
Can you open up internet explorer and enter in the VCenters IP into the browser on the server your trying to run ESXquery? Try to login to the Vcenter with the credentials. If your able to do that it is not a network issue.
